Combustion of air blast atomized spray flames

Abstract

Detailed experimental examination has been made of a series of air blast kerosene spray flames in secondary air flows in the wake of a stabilizer disc. Photography showed an initial dense spray region, with no combustion, surrounded by a gaseous diffusion flame. A laser diffraction technique was used for the measurement of droplet size distributions and their variation in the unignited spray. A laser anemometer with frequency shift, for reverse flow measurement, and a digital pulse counter was used for measurement of instantaneous velocity. Temperature was measured by miniature coated unshielded thermocouples and by suction pyrometer. Gas concentrations were measured in the flame by microprobes with analysis by gas phase chromatography. Droplet diameters decrease in the initial region of the spray due to secondary atomization, while further downstream, preferential vaporization of small droplets leads to increase in mean diameter of droplets. Increasing the air flow rate results in significant reduction in droplet diameter throughout the spray length. Velocities in spray flames are significantly higher than in nonburning sprays as a result of acceleration caused by increased volumetric flow rate due to phase change and temperature increase. Concentration measurements show lack of oxygen in the central core of the spray where carbon particles, carbon monoxide and hydrogen are formed.